Demand responsive hydraulic pump

Abstract

A hydraulic power steering system has a vane type pump which is operable to supply fluid to a power steering gear at a volumetric rate determined in part by the system pressure or system demand. The pump flow is partially bypassed through a valve member which is slidably disposed in the thrust plate of the pump. The thrust plate has a bypass aperture which communicates between the pump discharge and the pump inlet. The valve member is spring loaded to permit fluid communication through the apertures and is pressure biased by increasing system pressure to reduce the bypass flow and thereby increase system discharge flow.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. A demand responsive power steering pump comprising; inlet means for receiving fluid; outlet means for directing fluid from the pump and the fluid being subjected to various outlet pressure levels; vane pump means including rotor, vane and cam means for providing a plurality of pump chambers and a pair of end plate means for closing the axial ends of said chambers; one of said end plate means including valve means for bypassing some fluid from said pump chambers directly to said inlet means when the outlet pressure level is below a predetermined amount and for progressively decreasing the bypass flow as the outlet pressure level increases; said valve means comprising an annular chamber, annular valve means disposed in said chamber, passage means communicating one side of said annular valve means with said inlet means for permitting said bypassing of fluid, spring means urging said annular valve means to open said passage means and outlet fluid pressure acting on said annular valve means in opposition to said spring means to move said annular valve means to close said passage means. 
     
     
       2. A demand responsive power steering pump comprising; inlet means for receiving fluid; outlet means for directing fluid from the pump and the fluid being subjected to various outlet pressure levels; vane pump means including rotor, vane and cam means for providing a plurality of pump chambers and a pair of end plate means for closing the axial ends of said chambers; one of said end plate means including valve means for bypassing some fluid from said pump chambers directly to said inlet means when the outlet pressure level is below a predetermined amount and for progressively decreasing the bypass flow as the outlet pressure level increases; said valve means comprising an annular chamber, annular valve means disposed in said annular chamber, slot means in said annular valve means and apertures in said one end plate aligned with said slot means for permitting said bypassing of fluid, spring means urging said annular valve means to open said slot means, and outlet fluid pressure acting on said annular valve means in opposition to said spring means to move said annular valve means to close said apertures.